DESCRIPTION: (Adapted from the applicant's abstract.) This revised proposal focuses on the role of contrast in the mechanisms of stereoscopic depth perception, and has three main parts: First, a local contrast energy model for the mechanism of disparity extraction will be evaluated and developed as a model of stereroscopic processing. This model has been derived from a combination of quadrature filter responses to the dichoptic contrast images. Pairs of such filters for crossed and uncrossed disparities provide the local depth output in opponent fashion. The model is non-cooperative, minimizes the correspondence problem, and is easy to compute. The second set of experiments examines the stereoscopic effects of retinal image factors, including contrast and the contrast gain mechanism. The hypothesis that stereopsis is derived solely from the magnocellular system, and hence only from transient, achromatic aspects of the monouclar input, will be evaluated. Separate experiments are designed to test for the presence of a parvicellular influence in the form of sustained input to stereopsis and of chromatic input to stereomotion. Finally, the third set of experiments will use cyclopean stimuli in which the monocular information is functionally segregated from the disparity information, to allow the study of uncontaminated disparity processing. The monocular information will be restricted to high spatial frequencies while the disparity profile is limited to a nonoverlapping range of low spatial frequencies. These stimuli will be used to study cortical disparity interactions without contamination by monocular cues.